Abstract: When asymmetric cryptography techniques are used in wireless networks, the public
keys of the nodes need to be widely available and signed by a Certificate Authority (CA).
However, the existence of a single CA in large wireless networks such as mobile ad hoc
networks and wireless sensor networks can lead the hotspot problem and become a security
weakness. In this work, we propose a distributed technique to cache the public keys on
regular nodes. Due to the limited memory size that each node is allowed to dedicate
for key caching, only some keys can be cached. In our proposed technique, each node
caches the public keys of a mix of local and remote nodes. The local nodes are defined as
the nodes within the same neighborhood according to the transmission range, while the
remote nodes are the ones outside the range. Access to the public keys of other nodes is
possible based on a chain of trust. Multiple copies of public keys from different chains of
trusted nodes provide fault tolerance. We explain our technique in detail and investigate
its salient features in this work. An interesting observation is the need to balance caching
public keys of local nodes and remote nodes. We studied the optimum local/remote public
key caching ratios for different networks via investigating the availability of the number
of required public key copies. These simulation results showed that by balancing the
caching public keys with the optimum ratios, the availability of the required public keys
kept increasing and finally became stable. We also did the simulation about studying the
number of hops to find the first copies of required public keys. The results showed how
local/remote ratios affected the minimum number of hops for reaching the first copies.